Reactions of no with the Si(111) (7 × 7) surface: EELS, LEED and AES studies

Abstract

High-resolution vibrational electron energy loss spectroscopy, low-energy electron diffraction and Auger electron spectroscopy are used to study the reactions of NO with the Si(lll) (7x7) surface. At 300 K, NO is adsorbed dissociatively on the (7 × 7) surface in the disordered structure. The N and O atoms are chemisorbed in the on-top sites forming the SiN and SiO single bonds which are characterized by the vibrational losses at 118–125 and 100–105 meV, respectively. The maximum fractional coverages of N and O atoms are both θ ≈ 0.5. By heating the NO-saturated surface at 1150–1300 K, the adsorbed oxygen is removed from the surface and the N-covered surface is reconstructed to form the “(8 × 8)”-N structure which is characterized by the losses at 91 and 120 meV. This structure is proposed to arise from the overlayer in which each N atom is bonded to three Si atoms with the sp 3-like bonds forming a hexagonal lattice with unit mesh vectors of 8 11 times those of the unreconstructed Si(111) surface. As this surface is further heated at 1300–1350 K, the “quadruplet” structure which is characterized by the losses at 61 and 120 meV is formed. It is proposed that this structure has planar geometry with each N atom bonded to three Si atoms forming the sp 2-like bonds. The SiN bond length is estimated to be ≈1.7 Å. The local structure of the quadruplet surface is very similar to that of the bulk silicon nitride (Si 3N 4).